This application is based on application No. 99-44153 filed in the Korean Industrial Property Office on Oct. 12, 1999, the content of which is incorporated hereinto by reference.
(a) Field of the Invention
The present invention relates to an electrolyte for a rechargeable lithium battery and more particularly, to an electrolyte for a rechargeable lithium battery with good safety characteristics.
(b) Description of the Related Art
In recent years, the development of miniaturized portable electronics provokes needs for a rechargeable battery having a high capacity as well as a light weight. From the viewpoint of the capacity improvement per unit weight, the rechargeable lithium battery is preferably adopted because lithium has a high standard potential as well as a low electrochemical equivalent weight.
Safety characteristics are critical for rechargeable lithium batteries, and attempts to improve the safety characteristics have been made by modifying active materials, separators, battery systems or electrolytes. One approach has been to use a porous separator with a low melting point in the battery. The pores of the separator are easily blocked and lithium ions cannot pass through the pores. Another approach has been to design the battery to induce a short circuit when the internal pressure is raised due to gas generation.
Another approach is to use carbonate-based organic solvents in electrolytes. The carbonate-based organic solvents include cyclic carbonates such as ethylene carbonate and, propylene carbonate, linear carbonates such as dimethyl carbonate and, diethyl carbonate, and ethers such as tetrahydrofuran, ester and, ketone, or a mixture thereof. In particular, ethylene carbonate, propylene carbonate and ether are used.
However, the carbonate-based organic solvents have safety problems. The problems are caused by oxygen atoms in the carbonate-based organic solvents. During charge and discharge cycles, oxygen atoms are converted into oxygen gas or peroxide, resulting in an increase in internal pressure and possible explosion of the battery.
It is an object of the present invention to provide an electrolyte for a rechargeable lithium battery with good safety characteristics.
It is another object to provide the electrolyte for a rechargeable lithium battery that includes sulfur atoms.
These and other objects may be achieved by an electrolyte for a rechargeable lithium battery including at least one organic solvent and a lithium salt. The organic solvent is selected from thiocarbonate, thioester or thioether. The thiocarbonate, thioester or thioether is prepared by replacing oxygen atoms with sulfur atoms in carbonate, ester or ether, respectively.